Underwater diving masks are made up of a pair of lenses (or a single lens) supported by a rigid frame about which edge a part known as a facepiece is fixed, which facepiece is formed by a sort of casing made of a soft and elastically-yielding material, provided with openings for the lenses and the rear profile of which is sealedly applied to the face of the diver.
The rigid frame ensures the seal of the lenses and the rigidity of the mask.
The rear profile of the facepiece, which is to be applied to the diver's face, is shaped such as to be complementary as much as possible to the forehead, cheeks and lower part of the user's face.
In general the facepiece provides a projection able to receive the user's nose and inferiorly terminates below the nose, thus leaving the diver's mouth free for a snorkel, if one is being used.
The term “lens” is understood to mean a transparent membrane, generally flat, made of glass or another suitable material, which only in particular cases is effectively constituted by graduated lenses adapted to correcting defects in the user's sight.
The locking of the perimeter edge of the front openings of the facepiece about the lenses of the mask is generally realised in various known ways, and determines the formation of an open internal space of the mask delimited by the internal surface of the lenses and the part of the internal surface of the facepiece which encounters the internal surface of the lenses. This internal open space is closed by the face of the user wearing the mask.
In the locking closure known as “radial”, the perimeter edge of the front openings of the facepiece includes a groove facing towards the outside of the front openings in which the edge of the lenses is inserted, and the rigid frame is constituted by a single piece which locks with a force that acts in the plane of the lenses with the direction of the force facing towards the centre thereof.
In the locking closure known as “axial”, the perimeter edge of the front openings of the facepiece includes a flange facing towards the outside of the front openings, and the rigid frame is in general made up by two elements between which both the flange and the edge of the lenses are locked.
One of the drawbacks of the known-type diving masks consists in the fact that all the component elements ensuring the seal of the lenses and the rigidity of the mask determine a quite large internal space in the mask.
When the diver is swimming on the surface, this closed internal space is at atmospheric pressure. When the diver plunges below the surface, the pressure of such internal space must be compensated.
If the diver is provided with cylinders, the compensation is achieved by means of the air contained in the lungs which the diver can however top up with the gas contained in the cylinders. When on the other hand the diver dives in apnea, the compensation of the pressure in the internal space is done using the oxygen in his or her lungs but without any possibility of a top-up.
This leads to the need to reduce this internal space of divers' masks to a minimum.
To remedy this drawback it has been proposed to suitably position a filler material in the internal space of the mask. This expedient however adds one more element to the components of the mask, and thus increases the production cost and reduces the visual field of the user.
Alternatively the seal between the facepiece and the lenses can be ensured by gluing and overmoulding the edge of the openings in the facepiece to the lenses. In this case the rigidity of the mask is ensured by the glued or overmoulded frame. This solution enormously complicates the production process, which is longer and more expensive.
A further drawback of known-type diving masks consists in the fact that the solution used for the locking often makes the profile of the mask poorly hydro-dynamic in the connecting zone of the frame with the facepiece, with in particular the formation of large recesses between the frame and the facepiece which apart from constituting possible points of catching or dirt buildup, when the user swims can generate a turbulence in the water about the lenses, with a consequent deterioration of the sharpness of the visual field.